A buck might need 100,000 of such a girl (9)
I believe the answer is:
millicent
'a buck might need' is the definition.
The definition suggests a singular noun which matches the answer.
'100000 of such a girl' is the wordplay.
I cannot really understand how this works, but
'girl' could be 'millicen' and 'millicen' is found within the answer.
A single letter 't' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
(Other definitions for millicent that I've seen before include "Girl" , "Woman" .)